LAUGHTON
ELECTRONICS

The Microchek Press: a
specialized unit from Heath Custom Press

This article describes a
moderately
challenging class of printing presses I used to service, beginning with
buggy, early-issue machines which were essentially manufacturer's
prototypes. I also modified some of the machines' behavior in order to
better meet the production requirements of the customer.

Click to enlarge

Click to un-crop

Click to un-crop

To call this machine a
printing press would only tell half the story. It is really two
machines in one, specially built to print cheques for use by consumers
and business.

A key requirement
with cheque printing is
the sequential cheque number that appears on every sheet. The
sequential number is different for each individual sheet (although of
course other information such as the name and address stays the same
throughout a
run). The
Microchek press prints the customer information using a lithographic
master, and
prints the
sequential numbers using odometer-like
ratcheting numbering machines — all in a single operation.

Pneumatic cylinders are
used for actuating the various mechanisms, and the cylinders are
electronically controlled by an array of 24 volt air solenoids. The
original MicroChek wiring used a logic board with about thirty 74C00
series
CMOS chips. Timing signals originated from four optical switches
reading
timing disks mounted on the driveshaft. On the logic box, two sets of
thumbwheel switches were used to determine how many cheques and how
many (un-numbered) deposit sheets would be in each run. The numbering
options and
operating
sequences were hardwired, albeit with a degree of control via a
big 6-Pole,
12-position rotary Mode
Switch.

Repairs and
Modifications

These presses were
subject to predictable problems such as contamination of the optical
sensors and occasional shorts or bad connections where the press
wiring was subject to mechanical wear and tear. Early
production presses also had some design issues yet to be sorted out,
especially with regard to spurious operation of the logic.
Regarding this class of problems we were advised at one point to drill
a hole in
the concrete floor next
to every press and to install the biggest ground rod we could find!
I guess it's remotely possible that might've improved the situation
somewhat, but instead I
eradicated the problem by making wiring changes to ensure the 12 volt
supplies for the logic boxes were properly regulated, and by adding
noise filtering in the form of a simple RC wherever "outside world"
signals such as the
timing disks were brought into the logic box.

Over
the years I was repeatedly asked to make changes to the logic, simply
because the customer's
needs weren't always accommodated by the existing sequences. Changes
usually involved
poring over the schematics for a while, then tapping in to the logic
board and wiring in an extra gate, flip-flop or two.

Although
I would always oblige
the customer, I was never very keen on
making those
sorts of changes. To me it was blatantly obvious that a
microprocessor
ought to replace the inflexible hard-wired logic. A decade or so
later my view was vindicated when Heath Custom Press
discontinued the old style logic box and began supplying
microprocessors as standard equipment.